U.S. Pat. Nos. 2,972,363 and 3,438,410 disclose annular ring saws which employ apertured circular blades. These portable power saws permit a depth of cut greater than the radius of the blade.
The ring blades shown in these two patents are each peripherally driven by a power roller. Each blade has grooves formed in its upper and/or lower blade surfaces to accommodate blade guide rollers which maintain the blade virtual axial displacement as it is rotationally driven about its virtuall axis. Blade support rollers also act similarly on the blade's inner periphery to prevent radial displacement.
When a tree or other workpiece is being out by the power saw, the high speed blade encounters considerable resistance from the workpiece. These reaction forces act to shift the virtual axis of the ring blade in a direction opposite to that of blade rotation. In the two previously mentioned patents, these reaction forces are primarily opposed by the operator himself, resulting in fatigue, and by the blade guide and blade support rollers.
However, experience has shown that, due to the blade's high speed, the reaction forces tend to quickly heat and wear the grooves in the blade and to heat and wear the guide and support rollers themselves. This wearing action produces undesired blade vibration and poor cutting action. The solution of strengthening the blade, its grooves and the rollers is unsatisfactory for commercial reasons. Portable power saws of the ring type must be extremely light in order to compete with currently marketed saws, such as chain saws or circular saws which weigh as little as 61/2 lbs. Therefore, adding more weight and/or substituting more expensive heat dissipating materials is an unsatisfactory solution to the problem of dynamic operational instability and rapid blade groove and roller wear.
It is an object of this invention to provide means for dynamically stabilizing the power tool so that the aforementioned wear problems are eliminated or at least greatly reduced.
Another object is to provide dynamic stabilizing means which permits a reduction of the weight, power requirement and manufacturing cost of the power tool and especially which permits the use of a very thin saw blade, grinding wheel or other ring tool.
A further object is to provide a power tool which has many advanced features such as means for rapidly inserting and withdrawing the ring tool from its housing, means for self-lubricating the ring tool and the rollers, means for preventing the build-up of waste on the power tool's moving parts, and safety means causing the drive roller to slip on the ring tool when excessive load occurs.